Various types of reactors are used for atomic layer deposition (ALD) of thin films on semiconductor substrates. During ALD, a semiconductor substrate is exposed to alternating and sequential pulses of at least two mutually reactive reactants. The substrate temperature is chosen to be in a window above the reactants' condensation temperatures and below the reactant's thermal decomposition temperatures, so that during a reactant pulse a monolayer of the reactant adsorbs onto the substrate in a self-saturating manner without condensing or decomposing. After exposing the substrate to a first reactant, the process chamber is purged to remove any excess first reactant from the substrate and to remove any residual first reactant from the gas phase. The substrate is then exposed to a second reactant pulse, the second reactant being reactive with the first reactant.
Adequate purging and/or evacuating between the alternating reactant pulses is vital for good control of the deposition process. As purging takes time, the ALD process is generally a slow process.
Because of continual pressures within the semiconductor processing industry for increased throughput, there is a need for methods and apparatuses for ALD that allow efficient purging between subsequent reactant pulses, so that the purge time between pulses can be reduced and the overall deposition rate of the ALD process can be increased. In addition, because contaminating reactants can remain in a chamber by being deposited onto reactor walls there is also a need for reactors for ALD wherein deposition on the reactor walls is reduced or prevented.